KG-LLM: Add SPARQL query generation

[cmdoret]

Add the ability to generate and execute SPARQL queries.

Requirements:

• [x] Tune SPARQL config to allow 2 graphs: ontology and instances
• [x] Only embed ontology graph into ChromaDB
• [x] LLM for query generation with ontology chunks from chromaDB
• [x] Query execution via SPARQLWrapper